Cardiac Cycle

The mechanical events that occur to pump blood. This consists of 2 phases- diastole and systole. During Diastole the ventricles relax and fill. During Systole, the ventricles contract and expel.

The atria is filled with blood and the ventricle has just been drained which causes the AV valves to pop open and the atrial blood to flow down to the ventricles.

Second phase- the pressure between the atria and ventricle starts to equalize and blood turns from a flow to a trickle.

Last phase of the diastole, the atria is essentially empty but still a little blood to deliver. The atria contracts expelling the remainder of the blood into the ventricles. The ventricles now have a huge increase of pressure which forces the AV valve leaflets, which have been hanging down in the ventricles are now pushed up and slammed shut, ending the diastole. S1 is heard at this time. This kick provides 15%-30% ventricular filling and very important. Some heart rhythm abnormalities cause a loss of the atrial kick. This causes an immediate decrease in cardiac output.